This invention relates to methods and systems for bonding plastic parts together and, more particularly, to methods and systems for bonding plastic parts together utilizing infrared radiation.
When one wishes to attach plastic parts together, several processes exist to accomplish this. Among them are methods such as hot air bonding, sonic welding, vibration welding, adhesives, mechanical fasteners and infrared radiant heat.
U.S. Pat. No. 5,750,470 discloses a method of dielectrically heating an adhesive which, in turn, bonds plastic parts together.
Infrared radiant heat has certain advantages over the other types of processes. Generally, there is a desire to form a strong bond between the two parts quickly at a minimal cost. Additionally, it is preferable that during the bonding process nothing touches the surfaces to be bonded in order to assure uniform bonds from part-to-part and to reduce the cost of cleaning the bonding apparatus. Further, in many instances, it is preferable that no marring or distortion occur on the surface opposite the surface which is bonded. This surface is referred to as the xe2x80x9cviewingxe2x80x9d or xe2x80x9cclass Axe2x80x9d surface.
Infrared bonding, in general, can overcome many of these concerns. Infrared energy can be finitely pinpointed with a focal point or a mask to the exact area to be bonded in order to avoid overheating the plastic in adjacent areas that might cause unwanted distortion in the part. Infrared energy can heat the bonding surface to a high temperature, thus assuring that a strong bond is formed between the two parts. The bonding surface can be heated very quickly with infrared energy and the timing and amount of heat application can be precisely controlled. Further, with infrared heating, there need be no contact between the heat source and the bonding surfaces of the parts, in order to minimize cleaning requirements for the tooling.
Nonetheless, there are some drawbacks, in general, to using infrared heat to bond plastic parts together. In the case of automotive interior parts, for example, there are many parts made of plastic that are bonded to another part, but also need to have their viewing surfaces as distortion and mar free as possible since occupants of the vehicle will be able to see the surfaces. However, in the general application of focused infrared heat on the bonding surface in such applications, the xe2x80x9cclass Axe2x80x9d surface is oftentimes damaged. The finite focal point, while avoiding overheating adjacent areas, is too intense and harms many plastic parts during the heating process. An inherent difficulty to overcome in working with infrared radiant heat to bond plastic is to heat the bonding surfaces sufficiently without causing warpage, burning or marring of the xe2x80x9cclass Axe2x80x9d surfaces.
U.S. Pat. Nos. 3,383,265; 3,549,451; 4,265,954; 5,151,149; 5,244,525; 5,444,814 and 5,522,954 all disclose the use of infrared energy to bond or join plastic or polymeric materials together. The ""954 patent discloses the bonding of plastic interior automatic parts having xe2x80x9cclass Axe2x80x9d surfaces after each surface is exposed to infrared heat from an infrared heat source positioned between the surfaces.
U.S. Pat. No. 4,096,306 discloses a method of forming air-inflated cushioning material using two heat sealable films with air passages therebetween, which may be fused by xe2x80x9cinfrared black line sealing.xe2x80x9d
One prior art bonding process used hot air to activate a relatively expensive heat-activated adhesive. However, the use of hot air: 1) has a relatively long cycle time; 2) requires a relatively expensive heat-activated adhesive; and 3) requires a relatively large initial capital investment which equipment is relatively expensive to maintain.
The use of heat-activated adhesive to bond parts together is shown by the following U.S. Pat. Nos.: 5,228,108; 5,743,982; 5,486,252; 5,858,159; and 5,743,408.
An object of the present invention is to provide a method and system for bonding plastic parts together quickly and inexpensively without introducing deformities into the resulting assembly.
Another object of the present invention is to provide a method and system for bonding plastic parts together using infrared radiation which activates a heat-activated adhesive therebetween after propagating through at least one of the plastic parts.
Yet another object of the present invention is to provide a method and system for bonding plastic parts together wherein the bonds are quickly and inexpensively formed in a controlled fashion using infrared radiation which activates a heat-activated adhesive applied on an inner surface of at least one of the plastic parts.
In carrying out the above objects and other objects of the present invention, a method of bonding plastic parts together is provided. The method includes providing first and second plastic parts, applying a heat-activated adhesive on at least one inner surface of the plastic parts, positioning the plastic parts so that adhesive is located between inner surfaces of the plastic parts, and directing infrared radiation at the first plastic part so that the infrared radiation propagates through the first plastic part and is absorbed by the adhesive for a time sufficient to heat the adhesive to a desired temperature at which the adhesive is activated. The method also includes controlling the amount of heat applied to the adhesive by the infrared radiation. The activated adhesive bonds the plastic parts together.
Preferably, the method further includes the step of cooling the first plastic part. The step of cooling includes the step of blowing air at the first plastic part.
Also, preferably, the method further includes the step of generating a feedback signal based on the temperature of the adhesive wherein the step of controlling is based on the feedback signal.
Further in carrying out the above objects and other objects of the present invention, a system for bonding first and second plastic parts having a heat-activated adhesive located therebetween is provided. The system includes a first infrared lamp for emitting infrared radiation, a first base section for supporting the first infrared lamp adjacent the first plastic part, and a controller coupled to the first infrared lamp for controlling power supplied to the first infrared lamp so that the first infrared lamp emits infrared radiation which propagates through the first plastic part and is absorbed by the adhesive for a time sufficient to heat the adhesive to a desired temperature at which the adhesive is activated. The activated adhesive bonds the plastic parts together.
Preferably, the system further includes a first blower coupled to the controller for selectively supplying and interrupting a flow of forced air to the first plastic part to cool the first plastic part.
Also, preferably, the system further includes a temperature sensor coupled to the controller for sensing the temperature of the adhesive. The controller is responsive to the temperature sensor for controlling the power supplied to the first infrared lamp.
The first base section may have a first cavity formed therein in which the first infrared lamp is received and retained. A first cavity wall which defines the first cavity directs infrared radiation emitted by the first infrared lamp towards the first plastic part. The first base section may have a passage formed therein in fluid communication with the first cavity for conveying a flow of cooling air into the first cavity.
Still further in carrying out the above objects and other objects of the present invention, another system for bonding first and second plastic parts having a heat-activated adhesive located therebetween is provided. The system includes first and second infrared lamps for emitting infrared radiation. A first base section supports the first infrared lamp adjacent the first plastic part and a second base section supports the second infrared lamp adjacent the second plastic part. The system further includes a controller coupled to the first and second infrared lamps for controlling power supplied to the first and second infrared lamps so that the first infrared lamp emits infrared radiation which propagates through the first plastic part and is absorbed by the adhesive and the second infrared lamp emits infrared radiation which propagates through the second plastic part and is absorbed by the adhesive for a time sufficient to heat the adhesive to a desired temperature at which the adhesive is activated. The activated adhesive bonds the plastic parts together.
The above objects and other objects, features, and advantages of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.